Resonant wireless power transmitter circuit and control circuit and control method thereof

ABSTRACT

The present invention discloses a resonant wireless power transmitter circuit, which has an input impedance. The resonant wireless power transmitter circuit includes: a driver circuit coupled with a power supply, which includes at least a power switch; a switching resonant control circuit coupled with the driver circuit, such that the driver operates at a pre-determined or a variable resonant frequency; an adjustable impedance matching circuit coupled with the driver circuit, which includes at least a varactor; a transmitter circuit coupled with the impedance matching circuit and the driver circuit, which includes at least a transmitter coil; and an impedance control circuit coupled with the adjustable impedance matching circuit and the driver circuit, which provides an impedance control signal to control the reactance of the varactor, such that the input impedance of the resonant wireless power transmitter circuit is matched at the pre-determined or the variable resonant frequency.

CROSS REFERENCE

The present invention claims priority to U.S. 62/220,982, filed on Sep.19, 2015.

This is a Divisional of a co-pending application Ser. No. 15/095,087,filed on Apr. 10, 2016.

BACKGROUND OF THE INVENTION Field of Invention

The present invention relates to a resonant wireless power transmittercircuit. Particularly it relates to a resonant wireless powertransmitter circuit with an adjustable impedance matching circuit. Thepresent invention also relates to a control circuit and a control methodof the resonant wireless power transmitter circuit.

Description of Related Art

FIG. 1 shows a prior art resonant wireless power transmitter circuit.The resonant wireless power transmitter circuit 1 includes a powersupply VDD, two power switches Q1 and Q2, a transmitter coil L1, animpedance matching capacitor Cs, and a zero voltage switching tank 29(ZVS tank) which includes an inductor Lzvs and a capacitor Czvs. Thezero voltage switching tank 29 is connected with the power switch Q1 inparallel, and its resonant frequency is set to a low frequency forproviding an inductive load for the resonant wireless power transmittercircuit 1.

The prior art circuit shown in FIG. 1 have larger operation currentsthrough power switches Q1 and Q2 and a larger switching loss when thepower switches are switched to not conductive.

FIG. 2 shows an architecture according to another prior art disclosed byUS patent US2011/0133570. The power VTX_PWR of the prior art resonantwireless power transmitter circuit 2 can be lower, but in order toachieve this, it needs extra inductors and capacitors.

FIG. 3 shows another prior art resonant wireless power transmittercircuit disclosed by US patent US2012/0267960. The resonant wirelesspower transmission system 3 includes a transmitter circuit 24 and areceiver circuit 41. The transmitter circuit 24 includes a transmittercoil which has an inductance Lp. Rp stands for the parasitic resistanceof the transmitter circuit 24. Cp is a capacitor for impedance matching.Cd and a switch 820 connected with Cd form an impedance matching circuit23 for adjusting impedance matching. The receiver circuit includes areceiver coil which has an inductance Ls. Rs stands for the parasiticresistance of the receiver circuit 41. Cs is a capacitor for impedancematching. The prior art in FIG. 3 proposes multiple combinations of theswitch(es) and capacitor(s), and switches the switches to change thereactance of the impedance matching circuit, so as to adjust theresonant frequency of the resonant wireless power transmitter circuit.

The prior art in FIG. 3 has a drawback that there will be unavoidablequantization errors when adjusting the reactance by switching the switch820, and hence, there still will be power loss. To reduce thequantization errors requires more circuit devices, which increases thecost.

Compared to the prior art in FIG. 1, the present invention hasadvantages of a higher operation efficiency and that no inductor isrequired in the impedance matching circuit. Compared to the prior art inFIG. 2, the present invention requires less devices and the impedancematching circuit does not require an inductor.

Compared to the prior art in FIG. 3, the present invention hasadvantages of analog continuous adjustment in impedance matching tuning,no quantization error, lower power loss, and higher operationefficiency. And the present invention requires less devices.

The present invention provides a resonant wireless power transmittercircuit which has a capability of automatically adjusting the impedancematching and does not require an inductor in the impedance matchingcircuit.

SUMMARY OF THE INVENTION

From one perspective, the present invention provides a resonant wirelesspower transmitter circuit having an input impedance, comprising: adriver circuit, which is coupled to a power supply, wherein the drivercircuit includes at least a power switch; a switching resonant controlcircuit, which is coupled to the driver circuit, and configured tocontrol the driver circuit such that the driver circuit operates at apre-determined resonant frequency; an adjustable impedance matchingcircuit, which is coupled to the driver circuit, wherein the adjustableimpedance matching circuit includes at least one varactor, and has animpedance; a transmitter circuit, which is coupled to the adjustableimpedance matching circuit and the driver circuit, wherein thetransmitter circuit includes at least a transmitter coil, wherein thedriver circuit is configured to drive the transmitter coil by switchingthe power switch thereof; and an impedance control circuit, which iscoupled to the driver circuit and the adjustable impedance matchingcircuit, and configured to operably generate an impedance control signalto control a reactance of the varactor so as to control the impedance ofthe adjustable impedance matching circuit such that the input impedanceof the resonant wireless power transmitter circuit is matched at thepre-determined frequency.

In one embodiment, the adjustable impedance matching circuit includesone of the following combinations (A) and (B): wherein the adjustableimpedance matching circuit includes two or more varactors, and the twoor more varactors are connected in parallel, in series, or incombination of parallel and series; and wherein the adjustable impedancematching circuit includes one or more varactors and one or morecapacitors, and the one or more varactors and the one or more capacitorsare connected in parallel, in series, or in combination of parallel andseries.

In one embodiment, the adjustable impedance matching circuit isconfigured to operably generate the impedance control signal accordingto a signal related to a phase difference between a voltage and acurrent of the transmitter coil.

In one embodiment, the adjustable impedance matching circuit isconfigured to operably generate the impedance control signal accordingto a switching time signal of the power switch and a signal related to acurrent of the transmitter circuit or related to a current of the powerswitch.

In one embodiment, the adjustable impedance matching circuit isconfigured to operably generate the impedance control signal accordingto a phase difference between the switching time signal of the powerswitch and the signal related to the current of the transmitter circuitor related to the current of the power switch.

In one embodiment, the adjustable impedance matching circuit isconfigured to operably generate the impedance control signal accordingto a negative direction current of the power switch.

In one embodiment, the adjustable impedance matching circuit comprises:a negative direction current detection circuit, including: a firstcomparator, which is configured to operably compare the current of thepower switch and a first reference voltage to generate a negativedirection current signal; a delay circuit, which is configured tooperably delay the switching time signal of the power switch to generatea delayed switching time signal; a logic circuit, which is configured tooperably mask the negative direction current signal by the delayedswitching time signal to generate a negative direction current pulse;and a filter, which is configured to operably filter the delayedswitching time signal to generate a filter output signal as a candidateof the impedance control signal to control a reactance of the varactorso as to control the impedance of the adjustable impedance matchingcircuit such that the input impedance of the resonant wireless powertransmitter circuit is matched at the pre-determined frequency.

In one embodiment, the transmitter coil and the varactor and/or one ormore capacitors are connected in parallel, in series, or in combinationof parallel and series.

In one embodiment, the driver circuit is in one of the following forms:a half bridge driver circuit or a full bridge driver circuit or a classE driver circuit.

In one embodiment, the driver circuit is configured to be in the form ofa differential class E driver circuit, wherein the driver circuitincludes a first transmitter coil, and a second transmitter coilconnected in series, and wherein each of the first transmitter coil andthe second transmitter coil is connected with the varactor, and/or oneor more capacitors in parallel, in series, or in combination of paralleland series.

From another perspective, the present invention provides an impedancecontrol circuit, which is configured to operably control a resonantwireless power transmitter circuit which has an input impedance, whereinthe resonant wireless power transmitter circuit comprises: a drivercircuit, which is coupled to a power supply, wherein the driver circuitincludes at least a power switch; a switching resonant control circuit,which is coupled to the driver circuit, and configured to control thedriver circuit such that the driver circuit operates at a pre-determinedresonant frequency; and an adjustable impedance matching circuit, whichis coupled to the driver circuit, wherein the adjustable impedancematching circuit includes at least one varactor, and has an impedance;and a transmitter circuit, which is coupled to the adjustable impedancematching circuit and the driver circuit, wherein the transmitter circuitincludes at least a transmitter coil, wherein the driver circuit isconfigured to drive the transmitter coil by switching the power switchthereof; the impedance control circuit comprising: a phase differencedetermining circuit, configured to operably determines a phasedifference between a signal related to a current of the power switch (acurrent related signal) and a signal related to a switching time of thepower switch (a switching time related signal); and a control signalselection and output circuit which is coupled to the phase differencedetermining circuit, configured to operably select and output animpedance control signal according to a determining result of the phasedifference determining circuit, such that the input impedance of theresonant wireless power transmitter circuit is matched at thepre-determined frequency.

From another perspective, the present invention provides a method forcontrolling a resonant wireless power transmitter circuit which has aninput impedance, wherein the resonant wireless power transmitter circuitcomprises: a driver circuit, which is coupled to a power supply, whereinthe driver circuit includes at least a power switch; a switchingresonant control circuit, which is coupled to the driver circuit, andconfigured to control the driver circuit such that the driver circuitoperates at a pre-determined resonant frequency; and an adjustableimpedance matching circuit, which is coupled to the driver circuit,wherein the adjustable impedance matching circuit includes at least onevaractor, and has an impedance; and a transmitter circuit, which iscoupled to the adjustable impedance matching circuit and the drivercircuit, wherein the transmitter circuit includes at least a transmittercoil, wherein the driver circuit is configured to operably drive thetransmitter coil by switching the power switch thereof; the controlmethod comprising: generating an impedance control signal; andcontrolling a reactance of the varactor so as to control the impedanceof the adjustable impedance matching circuit such that the inputimpedance of the resonant wireless power transmitter circuit is matchedat the pre-determined frequency.

The objectives, technical details, features, and effects of the presentinvention will be better understood with regard to the detaileddescription of the embodiments below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a conventional resonant wirelesspower transmitter circuit and the related circuits thereof.

FIG. 2 shows a schematic diagram of another prior art resonant wirelesspower transmitter circuit.

FIG. 3 shows a schematic diagram of another prior art resonant wirelesspower transmission system which includes a resonant wireless powertransmitter circuit and a resonant wireless receiver circuit.

FIG. 4 shows a block diagram of an embodiment of the resonant wirelesspower transmission system according to the present invention.

FIG. 5 shows a schematic diagram of the equivalent circuit of a resonantwireless power receiver circuit coupling to the resonant wireless powertransmitter circuit according to the present invention.

FIG. 6 shows one embodiment of the resonant wireless power transmittercircuit according to the present invention.

FIG. 7 shows one embodiment of the resonant wireless power transmittercircuit according to the present invention.

FIGS. 8A and 8B show simulation waveforms of the circuit shown in FIG.7.

FIGS. 9A-9C show embodiments of the impedance control circuit andnegative direction current detection circuit thereof according to thepresent invention.

FIG. 10 shows simulation waveforms of the circuits shown in FIGS. 9B and9C.

FIGS. 11A-11D and 12A-12C show several embodiments of the resonantwireless power transmitter circuit according to the present invention.

FIG. 13A-13D show several embodiments of the variable capacitor circuitof the resonant wireless power transmitter circuit according to thepresent invention.

FIG. 14-16 show several embodiments of the resonant wireless powertransmitter circuit according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The drawings as referred to throughout the description of the presentinvention are for illustration only, to show the interrelations betweenthe circuits and the signal waveforms, but not drawn according to actualscale.

FIG. 4 shows one embodiment of the resonant wireless power transmissionsystem according to the present invention; the resonant wireless powertransmission system includes a resonant wireless power transmittercircuit 20 and a resonant wireless power receiver circuit 40.

The resonant wireless power transmitter circuit 20 shown in FIG. 4comprises a driver circuit 22 coupled to a power supply 21; anadjustable impedance matching circuit 23 coupled to the driver circuit22; a transmitter circuit coupled to the adjustable impedance matchingcircuit 23 and the driver circuit 22; an impedance control circuit 25,which is coupled to the adjustable impedance matching circuit 23 and thedriver circuit 22, and is configured to adjust the adjustable impedancematching circuit 23; and a switching resonant control circuit 26 coupledto the driver circuit 22. The power supply 21 may be an external powersupply (e.g. AC power supply) or an internal power supply (e.g. abattery) of the resonant wireless power transmitter circuit 20.

The resonant wireless power receiver circuit 40 includes a receivercircuit 41; an impedance matching circuit 42 coupled to the receivercircuit 41; a rectifier circuit 43 coupled to the impedance matchingcircuit 42; and a load 44 coupled to the rectifier circuit 43.

The wireless power transmission is achieved as thus. The resonantwireless power transmitter circuit in FIG. 4 converts the power suppliedby the DC or AC power supply 21 to a resonant frequency and transmit thepower to a wireless field 30 (for example but not limited to a magneticfield, an electric field or an electromagnetic field) through theresonant effect by the cooperation of the adjustable impedance matchingcircuit 23 and the transmitter circuit 24. The wireless powertransmitted to the wireless field 30 is received by the resonantwireless power receiver circuit 40 through for example but not limitedto coupling, induced by, or capturing the wireless power in the wirelessfield 30. The wireless power received is rectified by the rectifiercircuit 43 and supplied to the load 44.

Since the operation of the resonant wireless power transmission system 4shown in FIG. 4 is based on resonance effect, if the resonant frequencygenerated by the switching resonant control circuit 26 drifts from thepreset frequency, or if there is dislocation of the receiver circuit, orif there are multiple resonant wireless power receiver circuits coupledto receive the wireless power at the same time, off resonance couldhappen. If the off resonance is not corrected or controlled, it couldcause power loss. If off resonance happens in the resonant wirelesspower transmitter circuit 4, the current of the reactive components inthe resonant circuit (for example but not limited to the transmittercoil of the transmitter circuit 24, or the impedance matching capacitorof the adjustable impedance matching circuit 23) will lead (have anearlier phase) or lag (have a later phase) with respect to the voltagethereof. That is, there is a phase difference between the current andthe voltage of the resonant reactive components and the actual powertransmitted will decrease.

FIG. 5 shows an equivalent circuit (equivalent circuit 11) of theaforementioned resonant wireless power transmitter circuit coupling tothe resonant wireless power receiver circuit. The resonant wirelesspower transmitter circuit 20 includes a transmitter coil which has aninductance Lp; Rp which stands for the parasitic resistance of thetransmitter circuit 20; and Cp which is an impedance matching capacitor.The resonant wireless power receiver circuit 40 includes a receiver coilwhich has an inductance Ls; Rs which stands for the parasitic resistanceof the receiver circuit 40; and Cs which is an impedance matchingcapacitor; wherein RL is an equivalent load resistance.

Zeq is the reflection impedance of the transmitter side which is coupledfrom the receiver side and it can be shown as the equation below:

$Z_{eq} = \frac{\omega^{2}k^{2}L_{p}L_{s}}{R_{s} + {j\;\omega\; L_{s}} - {j\frac{1}{\omega\; C_{s}}} + R_{L}}$

wherein ω is the operating frequency in rad and k is the coupling factorbetween the transmitter coil and the receiver coil.

ZTX_IN is the equivalent input impedance of the transmitter side, whichincludes the equivalent inductor Lp, the equivalent resistor Rp, theimpedance matching capacitor Cp, and the reflection impedance of thetransmitter side which is coupled from the receiver side, Zeq. ZTX_INcan be shown as the equation below:

$Z_{TX\_ IN} = {R_{p} + {j\omega L_{p}} - {j\frac{1}{\omega C_{p}}} + \frac{\omega^{2}k^{2}L_{p}L_{s}}{R_{s} + {j\;\omega\; L_{s}} - {j\frac{1}{\omega\; C_{s}}} + R_{L}}}$

The current of the transmitter coil operating under the input voltageVin can be shown as the equation below:

$I_{TX\_ COIL} = \frac{V_{in}}{R_{p} + {j\;\omega\; L_{p}} - {j\frac{1}{\omega\; C_{p}}} + Z_{eq}}$

Hence, the input power can be expressed as:P _(IN)=Re{Z _(TX_IN) }×I _(TX_COIL) ²

When the input impedance of the resonant wireless power transmittercircuit 20 is matched, the imaginary part of the input impedance is zeroand the resonant wireless power transmitter circuit 20 can generate therequired transmission power and transmitter coil current under arelatively low input voltage.

If the input impedance of the resonant wireless power transmittercircuit 20 is not matched so that off resonance happens, the current ofthe reactive components in the resonant circuit (for example but notlimited to the transmitter coil of the transmitter circuit 24, or theimpedance matching capacitor of the adjustable impedance matchingcircuit 23 in FIG. 4) will lead (have an earlier phase) or lag (have alater phase) with respect to the voltage thereof. That is, there is aphase difference between the current and the voltage of the resonantreactive components and the actual power transmitted will decrease. Forproviding the same level of output power, the input voltage is requiredto be higher. Under this circumstance, the higher operating voltage andthe current which is phase-shifted from the operating voltage will causea larger power loss.

FIG. 6 shows one embodiment of the resonant wireless power transmittercircuit (resonant wireless power transmitter circuit 5) according to thepresent invention, wherein the resonant wireless power transmittercircuit 5 comprises a power supply 21; a driver circuit 22; anadjustable impedance matching circuit 23; a transmitter circuit 24 whichincludes a transmitter coil L1; and an impedance control circuit 25. Thedriver circuit 22 is for example but not limited to a half bridge drivercircuit as shown in FIG. 6, which includes power switches Q1 and Q2 andoperates at a pre-determined resonant frequency. The adjustableimpedance matching circuit 23 includes an impedance matching capacitorC1 and a variable capacitor circuit 231, wherein the impedance controlcircuit 25 determines the phase difference between the current and thevoltage of the resonant reactive components of the resonant wirelesspower receiver circuit 5 according to a switching time signal of aswitch (for example but not limited to a switching time signal of theswitch Q1) and a current related signal (for example but not limited toa current signal of the switch Q1), to generate an impedance controlsignal for controlling the variable capacitor circuit 231 to adjust thereactance of the adjustable impedance matching circuit 23, such that theinput impedance of the resonant wireless power transmitter circuit 5 ismatched under the pre-determined resonant frequency. The “pre-determinedresonant frequency” as used in the specification of the presentinvention may be a fixed value or an adjustable variable.

FIG. 7 shows one embodiment of the resonant wireless power transmittercircuit (resonant wireless power transmitter circuit 6), wherein theadjustable impedance matching circuit 23 includes an impedance matchingcapacitor C1 and a variable capacitor circuit 231; the variablecapacitor circuit 231 includes a varactor Dl, a DC bias resistor RB anda DC blocking capacitor CDC. In one embodiment, for example, thevaractor Dl may be a voltage controlled varactor of which thecapacitance and the reactance can be changed by applying differentlevels of reverse bias voltages. The impedance control circuit 25generates an impedance control signal to control the capacitance of thevaractor Dl and change its reactance, such that the input impedance ofthe resonant wireless power transmitter circuit 6 is matched at apre-determined resonant frequency.

In FIGS. 6 and 7, the current related signal used by the impedancecontrol circuit 25 for generating the impedance control signal is thecurrent signal related to the switch Q1. However, this is only oneembodiment. In other embodiments, it can be a current signal related tothe switch Q2 or the transmitter coil, instead of the current related tothe switch Q1. And, the switching time signal used by the impedancecontrol circuit 25 for generating the impedance control signal is thegate control signal of the switch Q1. Similarly, this is only oneembodiment. In other embodiments, it can be a switching time signalrelated to the switch Q2 instead of the switching time signal related tothe switch Q1, and the switching time signal is not limited to a gatecontrol signal of the switch, but can be any related signal whichcarries information of the switching time, for example but not limitedto a VDS (drain-source voltage) of the switch Q1 or Q2.

The phase difference between the current and the voltage of the resonantreactive components of the resonant wireless power transmitter circuits5 and 6 in FIGS. 6 and 7 can be determined by other ways, not limited tobeing based on the switching time signal and the current related signal.

FIG. 8A shows waveforms corresponding to the resonant wirelesstransmitter circuits 5 and 6 in FIGS. 6 and 7. As an example, when theoff resonance is caused by the impedance not-matching due to thereflection drift from the receiver side, with the same input power,I(Q1)_a and I(Q1)_b are currents of the switch Q1 under matchedimpedance and under not-matched impedance respectively, and I(L1)_a andI(L1)_b are currents of the transmitter coil L1 under matched impedanceand under not-matched impedance respectively. The current through theswitch Q1 of the resonant wireless transmitter circuits 5 and 6 in FIGS.6 and 7, when the switch Q1 is conductive, is the current of thepositive half cycle of the resonant sinewave. When the impedance ismatched, as shown by I(Q1)_a, the current of the switch Q1 has awaveform which is very close to a perfect semi-sinusoidal waveform(positive half cycle of the resonant sinewave). On the other hand, ifthe impedance is not matched, there will be a phase difference betweenthe current and the voltage of the resonant reactive components in theresonant wireless transmitter circuits 5 and 6, and hence, as shown byI(Q1)_b, the current of the switch Q1 has an imperfect semi-sinusoidalwaveform which is off-phase, that is, apart of the upper half sinewaveat the leading edge is missing and there is an extra part of the lowerhalf sinewave, which means a current toward an opposite direction(negative direction current). That is, a part of the current whichoriginally should be flowing toward a direction (positive directioncurrent) for power transmission flows toward the opposite direction (thenegative direction current) to deteriorate the efficiency of the powertransmission.

In addition, as shown in FIG. 8A, with the same input power, thetransmitter coil current I(L1)_b (dashed line) under not-matchedimpedance is smaller than the transmitter coil current I(L1)_a (solidline) under matched impedance, and there is a phase difference betweenthese two currents. As shown in FIG. 8B, it requires a larger current ofthe power switch Q1 (i.e. I(Q1)_b>I(Q1)_a) for the current oftransmitter coil L1 to be the same (i.e. I(L1)_a≈I(L1)_b). The aboveexplains that when the input impedance is not matched, the resonantwireless power transmitter circuits 5 and 6 will have larger power lossand lower power transmission efficiency.

FIG. 9A shows one embodiment of the impedance control circuit (impedancecontrol circuit 25′) according to the present invention, which includesa phase difference determining circuit 258 and a control signalselection and output circuit 259. The phase difference determiningcircuit 258 determines the phase difference between a current relatedsignal (For example, in the embodiments of FIGS. 6 and 7, the currentrelated signal may be a signal related to the current of the switch Q1,but may also be a signal related to the current of the switch Q2 or thetransmitter coil current) and a switching time related signal (Forexample, in the embodiments of FIGS. 6 and 7, the switching time relatedsignal may be a switching time signal related to the switch Q1 or theswitch Q2, e.g. a gate control signal or a drain-source voltage signalthereof). And, the control signal selection and output circuit 259selects and outputs the impedance control signal VCTRL according to thedetermination result from the phase difference determining circuit 258.The impedance control signal VCTRL may be an analog signal or a digitalsignal. In a preferred embodiment, VCTRL is an analog signal.

FIG. 9B is one specific embodiment of the impedance control circuitaccording to the present invention (impedance control circuit 25″). Theimpedance control circuit 25″ includes a negative direction currentdetection circuit 251, a filter 252, a comparator 253 and a multiplexer254, wherein the negative direction current detection circuit 251receives a switching time signal (for example but not limited to thegate control signal VGS of the switch Q1 in the embodiments of FIGS. 6and 7 and a current related signal (for example but not limited to acurrent sensed signal VIDS of the switch Q1, which indicates the currentthrough the switch Q1) to generate a negative direction current pulseVREV. The filter 252 generates a filtered negative direction currentpulse VREV′ by filtering the negative direction current pulse VREV. Thecomparator 253 compares the filtered negative direction current pulseVREV′ and a reference voltage VREF1. The multiplexer 254 selects thefiltered negative direction current pulse VREV′ or a reference voltageVREF1 as the impedance control signal VCTRL. In this embodiment, thenegative direction current detection circuit 251 corresponds to theaforementioned phase difference determining circuit 258, whereas thefilter 252, the comparator 253 and the multiplexer 254 correspond to theaforementioned control signal selection and output circuit 259.

In the aforementioned embodiment, the reference voltage VREF1 is used asan input of the comparator 253 (i.e. a signal to be compared with thefiltered negative direction current VREV′) and also as one of thecandidates to be selected by the multiplexer 254. In another embodiment,another reference voltage (not shown) may be used to replace thereference voltage VREF1 as one of the candidates to be selected by themultiplexer 254, i.e., the comparator 253 compares the filtered negativedirection current pulse VREV′ and the reference voltage VREF1, andselects the filtered negative direction current pulse VREV′ or theaforementioned other reference voltage (not shown) as the impedancecontrol signal VCTRL.

Please refer to FIG. 9C, which shows one embodiment of the negativedirection current detection circuit 251′ according to the presentinvention. The negative direction current detection circuit 251′includes a comparator 2511, a delay circuit 2512, and a logic circuit2513. The comparator 2511 compares a current related signal VIDS and areference voltage VREF2 to generate a negative direction current signalVREV″. The delay circuit 2512 delays the aforementioned switching timesignal VGS of the power switch to generate a delayed switching timesignal VGS_D. The logic circuit 2513 uses the delayed switching timesignal VGS_D to mask the negative direction current signal VREV″, togenerate a negative direction current pulse VREV.

Note that there are various embodiments of the impedance control circuitand the embodiment shown in 9B is only one of them. In one embodiment asan example, a mapping circuit (not shown) may replace the filer 252, thecomparator 253 and the multiplexer 254 to generate an output signal bymapping the input signal.

FIG. 10 shows waveforms of the circuits in FIGS. 6, 7, 9B, and 9C. Underfor example but not limited to the off resonance condition caused by theimpedance not-matching due to the reflection drift from the receiverside, in the beginning, because the impedance is not matched, VIDS (i.e.a current related signal of current I(Q1) of the switch Q1) presents animperfect semi-sinusoidal waveform with a phase difference (i.e. a partof the upper half sinewave at the leading edge is missing and there isan extra part of the lower half sinewave, which means a negativedirection current). The signal VIDS is masked by the delayed switchingtime signal VGS_D whereby a negative direction current pulse VREV isgenerate. And the impedance control circuit 25 as shown in FIGS. 6, 7,9A, and 9B generates the impedance control signal VCTRL according to thenegative direction current pulse VREV. The adjustable impedance matchingcircuit 23 adjusts the capacitance of the varactor, and hence thereactance of the adjustable impedance matching circuit 23 and theimpedance of the resonant wireless power transmitter circuit are therebyadjusted. As shown by the above, a negative feedback loop is formed suchthat the input impedance of the resonant wireless power transmittercircuit can be adjusted to be matched automatically, continuously, andin analog form, as the wireless power is being transmitted. Hence, asshown in FIG. 10, the impedance control signal VCTRL is automaticallyadjusted such that the current through the power switch, as indicated bythe signal VIDS, gradually becomes a perfect semi-sinusoidal waveformwithout any phase difference and the negative direction current pulseVREV gradually becomes silent. This means that the resonant wirelesspower transmitter circuit originally in off resonance state has adjusteditself to a preferred resonant state automatically. That is, the inputimpedance of the resonant wireless power transmitter circuit isautomatically adjusted, continuously and in analog form, to be matchedas the wireless power is being transmitted. The phase difference betweenthe current and the voltage of the resonant reactive components (forexample but not limited to the transmitter coil) approaches zero so thatthe resonant wireless power transmitter circuit has a much highertransmission efficiency and a much lower power loss.

In the aforementioned example of automatic adjustment of the impedancematching, the root cause of impedance not-matching is the reflectiondrift from the receiver side, which is only an illustrative example.Because the adjustment of the impedance in the present invention is notsimply based on detecting an amount of the a system current or a changeof the system current, but based on signals related to the phasedifference between the current and the voltage (for example but notlimited to a switching time related signal and a current related signalof a switch) of the resonant reactive components (for example but notlimited to the transmitter coil and/or the impedance matching capacitor)of the resonant wireless power transmitter circuit, hence, for adifferent root cause to cause off resonance such as but not limited toan operation error in an oscillator (not shown) of the switchingresonant control circuit 26 as shown in FIG. 4, the present inventioncan still be applied to automatically adjust the resonant wireless powertransmitter circuit to a preferred resonant state

The aforementioned adjustable impedance matching circuit 23 is notlimited to the example in FIG. 6. FIG. 11A-11D show various otherembodiments of the adjustable impedance matching circuit and thetransmitter circuit according to the present invention, wherein thetransmitter circuit 24 is for example a single transmitter coil, and thevariable capacitor circuit 231 of the adjustable impedance matchingcircuit 23 may be coupled to the transmitter circuit 24 in parallel, inseries or in combinations of parallel and series.

In FIG. 11A, the adjustable impedance matching circuit 23 is coupled tothe transmitter circuit 24 in series, wherein the adjustable impedancematching circuit 23 includes a variable capacitor circuit 231 and animpedance matching capacitor C1, wherein the variable capacitor circuit231 and the impedance matching capacitor C1 are coupled in parallel.

In FIG. 11B, the adjustable impedance matching circuit 23 is coupled tothe transmitter circuit 24 in series, wherein the adjustable impedancematching circuit 23 includes a variable capacitor circuit 231.

In FIG. 11C, the adjustable impedance matching circuit 23 is coupled tothe transmitter circuit 24 in parallel, wherein the adjustable impedancematching circuit 23 includes a variable capacitor circuit 231 and animpedance matching capacitor C1, wherein the variable capacitor circuit231 and the impedance matching capacitor C1 are coupled in parallel.

In FIG. 11D, the adjustable impedance matching circuit 23 is coupled tothe transmitter circuit 24 in parallel, wherein the adjustable impedancematching circuit 23 includes a variable capacitor circuit 231.

In FIG. 12A, the adjustable impedance matching circuit 23 is coupled tothe transmitter circuit 24 in a combination of parallel and series,wherein the adjustable impedance matching circuit 23 includes variablecapacitor circuits 231 and 232.

In FIG. 12B, the adjustable impedance matching circuit 23 is coupled tothe transmitter circuit 24 in a combination of parallel and series,wherein the adjustable impedance matching circuit 23 includes a variablecapacitor circuit 231 and an impedance matching capacitor C1, whereinthe transmitter circuit 24 and the impedance matching capacitor C1 arecoupled in parallel.

In FIG. 12C, the adjustable impedance matching circuit 23 is coupled tothe transmitter circuit 24 in a combination of parallel and series,wherein the adjustable impedance matching circuit 23 includes a variablecapacitor circuit 231 and an impedance matching capacitor C1, whereinthe transmitter circuit 24 and the variable capacitor circuit 231 arecoupled in parallel.

The aforementioned various possible combinations of the adjustableimpedance matching circuit 23 and the transmitter circuit 24 are onlyfor illustration purpose but not for limiting the scope of the presentinvention.

In one embodiment, for example, the varactor (e.g. Dl in FIG. 13A-13D)may be a voltage controlled varactor of which the capacitance can beadjusted by applying different levels of reverse bias voltage. Since theaforementioned voltage controlled varactor requires DC bias foroperation and control, the variable capacitor circuit containing suchvaractor(s) may include DC bias resistor(s) or DC blocking capacitor(s)in for example but not limited to the following forms, depending on theactual application conditions.

In FIG. 13A, the variable capacitor circuit 233 includes a varactor Dl,a DC bias resistor RB and a DC blocking capacitor CDC.

In FIG. 13B, the variable capacitor circuit 234 includes a varactor Dland a DC bias resistor RB.

In FIG. 13C, the variable capacitor circuit 235 includes a varactor Dland a DC blocking capacitor CDC.

In FIG. 13D, the variable capacitor circuit 236 includes a varactor Dl.

Instead of the half bridge driver circuit 22 shown in FIGS. 6 and 7, thedriver circuit 22 of the resonant wireless power transmitter circuit 20in FIG. 4 may be for example but not limited to the driver circuitsshown in FIGS. 14-16. In FIG. 14, the driver circuit 22 is a full bridgedriver circuit which includes four power switches Q1, Q2, Q3, and Q4.The half loop circuit formed by the transmitter circuit 24 and theadjustable impedance circuit 23 are connected to the node between Q1 andQ3 and the node between Q2 and Q4. In FIG. 15, the driver circuit 22 isa class E power amplifier which includes a power switch Q1, inductors L2and L3, and a capacitor C3. In FIG. 16, the driver circuit 22 is adifferential class E power amplifier which includes two symmetricalclass E power amplifiers, including two power switches Q1 and Q2, twoinductors L3 and L4, and two capacitors C3 and C4, and the transmittercircuit 24 includes two symmetrical transmitter coils L1 and L2.

The present invention has been described in considerable detail withreference to certain preferred embodiments thereof. It should beunderstood that the description is for illustrative purpose, not forlimiting the scope of the present invention. It is not limited for eachof the embodiments described hereinbefore to be used alone; under thespirit of the present invention, two or more of the embodimentsdescribed hereinbefore can be used in combination. For example, two ormore of the embodiments can be used together, or, a part of oneembodiment can be used to replace a corresponding part of anotherembodiment. In view of the foregoing, those skilled in this art canreadily conceive variations and modifications within the spirit of thepresent invention. For example, to perform an action “according to” acertain signal as described in the context of the present invention isnot limited to performing an action strictly according to the signalitself, but can be performing an action according to a converted form ora scaled-up or down form of the signal, i.e., the signal can beprocessed by a voltage-to-current conversion, a current-to-voltageconversion, and/or a ratio conversion, etc. before an action isperformed. The spirit of the present invention should cover all such andother modifications and variations, which should be interpreted to fallwithin the scope of the following claims and their equivalents.

What is claimed is:
 1. An impedance control circuit, which is configuredto operably control a resonant wireless power transmitter circuit whichhas an input impedance, wherein the resonant wireless power transmittercircuit comprises: a driver circuit, which is coupled to a power supply,wherein the driver circuit includes at least a power switch; a switchingresonant control circuit, which is coupled to the driver circuit, andconfigured to control the driver circuit such that the driver circuitoperates at a pre-determined resonant frequency; and an adjustableimpedance matching circuit, which is coupled to the driver circuit,wherein the adjustable impedance matching circuit includes at least onevaractor, and has an impedance; and a transmitter circuit, which iscoupled to the adjustable impedance matching circuit and the drivercircuit, wherein the transmitter circuit includes at least a transmittercoil, wherein the driver circuit is configured to drive the transmittercoil by switching the power switch thereof; the impedance controlcircuit comprising: a phase difference determining circuit, configuredto operably determine a phase difference between a signal related to acurrent of the power switch (a current related signal) and a signalrelated to a switching time of the power switch (a switching timerelated signal); and a control signal selection and output circuit whichis coupled to the phase difference determining circuit, and configuredto operably select and output an impedance control signal according to adetermining result of the phase difference determining circuit, suchthat the input impedance of the resonant wireless power transmittercircuit is matched at the pre-determined frequency.
 2. The impedancecontrol circuit for controlling a resonant wireless power transmittercircuit of claim 1, wherein the adjustable impedance matching circuitincludes one of the following combinations (A) and (B): (A) wherein theadjustable impedance matching circuit includes two or more varactors,and the two or more varactors are connected in parallel, in series, orin combination of parallel and series; and (B) wherein the adjustableimpedance matching circuit includes one or more varactors and one ormore capacitors, and the one or more varactors and the one or morecapacitors are connected in parallel, in series, or in combination ofparallel and series.
 3. The impedance control circuit for controlling aresonant wireless power transmitter circuit of claim 1, wherein thephase difference between the current related signal and the switchingtime related signal relates to a signal which is related to a phasedifference between a voltage and a current of the transmitter coil. 4.The impedance control circuit for controlling a resonant wireless powertransmitter circuit of claim 1, wherein the phase difference determiningcircuit determines the phase difference according to a negativedirection current of the power switch.
 5. The impedance control circuitfor controlling a resonant wireless power transmitter circuit of claim4, wherein the phase difference determining circuit includes: a firstcomparator, which is configured to operably compare the current of thepower switch and a first reference voltage to generate a negativedirection current signal; a delay circuit, which is configured tooperably delay the switching time signal of the power switch to generatea delayed switching time signal; a logic circuit, which is configured tooperably mask the negative direction current signal by the delayedswitching time signal to generate a negative direction current pulse;and a filter, which is configured to operably filter the delayedswitching time signal to generate a filter output signal to represent adetermining result of the phase difference determining circuit.
 6. Theimpedance control circuit for controlling a resonant wireless powertransmitter circuit of claim 5, wherein the control signal selection andoutput circuit includes: a second comparator, which is configured tooperably compare the filter output signal and a second reference voltageto generate a selection signal; and a multiplexer, which is configuredto operably to select the filter output signal or the second referencevoltage, or select the filter output signal or a third referencevoltage, to be the impedance control signal.